Conventionally, a vehicle is provided with an airbag device, which inflates a bag by quickly supplying gas when a rapid deceleration occurs due to, for example, a car crash. The airbag device includes an inflator for quickly supplying gas when the device is activated and a bag inflated by the gas from the inflator for protecting passengers. The inflator incorporates an igniter, a gas generating agent burned in an explosive-like manner by the heat generated by the igniter, and a filter. The filter collects and cools solid or liquid residue contained in hot gas generated through combustion of the gas generating agent. The filter is configured normally by a coil type filter, which is formed by winding a circular wire or a deformed wire, such as a square wire, formed of metal (hereinafter, referred to as “a wire”) in a layered manner for defining a meshed cylindrical body. When gas or liquid passes through the mesh defined by the wire, the substance is cooled and filtered by the coil type filter such that a residue is recovered.
After winding the wire of this type of filter, overlapping portions of the wire are bonded together by, normally, thermal treatment (sintering). In this manner, the filtration performance of the filter is maintained by preventing the mesh from being deformed due to expansion of the wire or an impact caused by the gas passing through the mesh.
Particularly, a filter serving as a filtering member for an airbag is exposed to extremely hot gas. It is thus necessary to employ a bonding method that ensures a relatively high bonding strength. Therefore, for improving the bonding strength, it has been proposed that the sintering be conducted at a higher temperature, or for a prolonged time, or in a modified atmosphere (see Japanese Laid-Open Patent Publication No. 2001-171472).
However, in accordance with the fabrication method for a filter for an airbag inflator described in the aforementioned publication, it is necessary to modify the corresponding equipment for obtaining a higher sintering temperature or changing the sintering atmosphere. Such modification requires a relatively large cost, thus increasing the manufacturing cost. Further, the prolonged processing time decreases productivity.
Accordingly, in order to solve the aforementioned problems of the prior art, it is an objective of the present invention to provide a fabrication method for a filtering member by which the bonding strength of a wire forming a mesh is improved with relatively low cost and relatively high efficiency.